Supporting the Linux desktop

I recently interviewed for an IT position at a tech company recently, and despite doing almost exclusively Windows support for over a decade, I did surprisingly well on the Linux part of the interview. I had been candid with them upfront about my limited exposure to CentOS and Ubuntu, and that it had been about 15 years since I had trained and worked with Solaris, but I was able to answer most of their questions or at least get close enough to the answer that they were willing to give me credit. I didn't get the job, however, so now I'm wondering what I could focus on to do better if a similar position or situation should arise. Are there certain problems that crop up regularly that constitute the bulk of Linux bread-and-butter work? Is there a generally accepted set of tasks or commands a tech should know? What does a typical day supporting a desktop distro look like, if there is such a thing? Let me know what your experience has been. Thanks.

What does a typical day supporting a desktop distro look like, if there is such a thing?

Last place I worked that had Linux desktops that weren't managed by the person using them was like RHEL5 in 2008...

I don't know exactly what a "typical" Linux desktop deployment looks like, but old venerable books are "The Practice of System and Network Administration" by Limoncelli and "UNIX and Linux System Administration Handbook" by Nemeth.

But today you should probably know how to handle systemd. It's not hard, it's just a little different and new.

Depends on what you have to do, how many you have to manage. I would say that you want at least a RHCSA level of knowledge. If you are doing a lot of deploying, then you want the advanced certificate on system management and deployment (red hat satellite).